ICQ
See whom of your friends is online and communicate directly.
Not in use anymore, since there is Skype, a pity, it was a nice programm.
(New is ICQ 5 lite)
http://www.mirabilis.com
Trilian
Or what do you think of Trillian?
It can connect you at the same time to:
ICO, MSN, AIM, Yahoo and IRC
(the sounds are better too)
http://www.ceruleanstudios.com/